What is ipamorelin? What published studies say it does in the body

What is ipamorelin?

Ipamorelin is a synthetic pentapeptide, a chain of five amino acids (Aib-His-D-2-Nal-D-Phe-Lys-NH2), made by a research group in Denmark and first described in 1998 (Raun et al., European Journal of Endocrinology, 1998). Ipamorelin belongs to the class of growth hormone secretagogues, which are compounds that make the pituitary gland release growth hormone. The FDA's review notes that ipamorelin contains unnatural amino acids, meaning building blocks not found in the body's own proteins. The FDA found that ipamorelin is not a component of any FDA-approved drug (FDA review, 19 August 2024).

The name of the class tells you where ipamorelin sits. A secretagogue is something that prompts release. Growth hormone releasing peptides, or GHRPs, are a family of such compounds. Raun and colleagues report that ipamorelin came out of a chemistry programme on a series of compounds that lacked the central Ala-Trp pair of an earlier member of the family, GHRP-1 (Raun et al., 1998).

Other identifiers appear in the papers. The compound's research code is NNC 26-0161 (Johansen et al., Xenobiotica, 1998). Its formula is C38H49N9O5 and its weight is 711.9 g/mol (PubChem compound 9831659). Later clinical work is listed on ClinicalTrials.gov as NCT00672074 and NCT01280344.

Evidence limits

What do the published studies of ipamorelin not show?

Three limits come up again and again. First, the human trial enrolled patients recovering from bowel surgery, so its results say little about healthy people. Second, a larger Phase 2 trial of 320 enrolled patients, NCT01280344, is listed as completed in 2014, yet its ClinicalTrials.gov record shows no posted results on 14 October 2026. Third, the animal studies differ from the human trials in species and route, so a result in a rat does not predict a result in a person.

A 2020 review of growth hormone secretagogues in men with low testosterone names the same gap. It describes a 'paucity of data' on the clinical effects of these compounds, ipamorelin among them, and it ran no new trial (Sinha et al., Translational Andrology and Urology, 2020).

What does research show ipamorelin does in the body?

Ipamorelin raised growth hormone in rat pituitary cells, in anaesthetised rats and in conscious pigs, with a potency and strength similar to the older peptide GHRP-6; these are cell and animal results that do not establish a human result, and the abstract gives no animal count (Raun et al., European Journal of Endocrinology, 1998). In eight healthy men at each of five infusion levels, growth hormone rose to a single peak about 0.67 hours after the infusion and fell to very low levels; the study measured hormone levels, not clinical outcomes (Gobburu et al., Pharmaceutical Research, 1999).

Growth hormone, or GH, is the hormone your pituitary releases in pulses. GH in turn stimulates production of IGF-1, a second hormone linked to growth (FDA briefing document, 29 October 2024). The FDA's review says ipamorelin acts mainly through ghrelin receptors on nerve cells that control GH release. It also notes that ghrelin receptors occur in organs that include the heart, lung, liver, kidney, pancreas, intestine, adrenal gland, testis, fat tissue and stomach. A receptor's presence in an organ shows where the receptor is found, not what ipamorelin does there.

The animal work covers a wide field, and each result belongs to its model only. In rats after surgery, with no count in the abstract, ipamorelin sped up bowel movement, an animal finding that does not establish a human result (Venkova et al., Journal of Pharmacology and Experimental Therapeutics, 2009). In adult female rats, with no count in the abstract, ipamorelin increased the growth rate of long bone, again an animal finding that does not establish a human result (Johansen et al., Growth Hormone & IGF Research, 1999). In pancreas tissue fragments taken from normal and diabetic rats and kept in a dish, with no count in the abstract, it raised insulin release, a tissue result that does not establish a human result (Adeghate and Ponery, Neuro Endocrinology Letters, 2004).

Which receptor does ipamorelin act on?

Ipamorelin acts on the ghrelin receptor, also called the growth hormone secretagogue receptor. Researchers cloned this receptor from the pituitary gland and hypothalamus of pigs and humans in 1996 and showed it is the target of synthetic secretagogues, in laboratory work on cloned tissue (Howard et al., Science, 1996). In 1999 a Japanese team purified its natural partner, ghrelin, a 28-amino-acid peptide, from rat stomach (Kojima et al., Nature, 1999). In rat and pig experiments with blocking agents for the GHRP and GHRH receptors, ipamorelin, like GHRP-6, released growth hormone through a GHRP-like receptor, which is an animal finding that does not establish a human result, with no count in the abstract (Raun et al., 1998).

GHRH, or growth hormone-releasing hormone, is a different signal from the hypothalamus that also prompts GH release. Compounds such as sermorelin and tesamorelin copy GHRH. Compounds such as ipamorelin copy ghrelin. How ipamorelin differs from tesamorelin, sermorelin and the other secretagogues sets the two families side by side.

A 1998 review of earlier studies covers how secretagogues and GHRH act together (Ghigo et al., Annals of Medicine, 1998); this page reports no result from it. No study opened for this page tested that pairing with ipamorelin.

Is ipamorelin selective? What did studies find about prolactin and cortisol?

In the original pig study, ipamorelin raised growth hormone without raising ACTH or cortisol above the levels that GHRH produced, and none of the compounds tested changed FSH, LH, prolactin or TSH in pigs; selectivity is therefore a finding from pigs, with no count in the abstract, that does not establish a human result (Raun et al., European Journal of Endocrinology, 1998). The same study found that GHRP-6 and GHRP-2 raised ACTH and cortisol in the pigs, an animal result that does not establish a human result, with no count in the abstract (Raun et al., 1998). Human studies of ipamorelin that report cortisol and prolactin values were not found for this page.

ACTH is the pituitary signal that tells the adrenal glands to make cortisol, the body's main stress hormone. In seven healthy volunteers, hexarelin, an older peptide of the same class, led overnight to higher growth hormone, prolactin, ACTH and cortisol than placebo, in a small study of a different compound (Frieboes et al., Psychoneuroendocrinology, 2004). A diagnostic study in 49 patients and 20 healthy controls used GHRP-6 as a probe of the stress-hormone axis because it is a known activator of that axis, and it was not a study of ipamorelin (Alaioubi et al., Hormone and Metabolic Research, 2010).

A 2026 review discusses ipamorelin and other pituitary-adrenal axes (Dominikowski et al., Frontiers in Endocrinology, 2026). This page does not report its summary of human studies, because the underlying human study and its cohort were not checked; the abstract of the 1999 healthy-volunteer study reports only ipamorelin and growth hormone levels, and its full text was not opened for this page. The FDA's 2024 review discusses ACTH and cortisol with reference to Raun et al., 1998, the pig study above, and a 2001 paper; the pig result is an animal result that does not establish a human result (FDA briefing document, 29 October 2024).

What clinical trials of ipamorelin exist?

The searches for this page identified the 1999 volunteer study and two Phase 2 bowel-surgery trials; an observational registry record is described below. A 1999 study in eight healthy men at each of five infusion rates followed how ipamorelin and growth hormone levels moved over time, and measured hormone levels only (Gobburu et al., Pharmaceutical Research, 1999). A Phase 2 trial in 117 enrolled bowel-surgery patients, NCT00672074, found no significant difference from placebo in time to first tolerated meal, in one small patient group (Beck et al., International Journal of Colorectal Disease, 2014). A larger Phase 2 trial, NCT01280344, enrolled 320 patients and shows no posted results on ClinicalTrials.gov (checked 14 October 2026).

A PubMed search for ipamorelin on 14 October 2026 returned 55 records, and two are indexed as clinical trials: the 1999 volunteer study and the 2014 surgery trial. The volunteer study used five infusion rates, with eight healthy men at each level, and the FDA's summary says that paper did not state whether adverse events occurred (FDA briefing document, 29 October 2024). In the placebo-controlled surgery trial of up to a week in 117 enrolled bowel-surgery patients, the authors judged ipamorelin well tolerated, in a small trial in one patient group (Beck et al., 2014).

Both Phase 2 trials were for recovery of gut function after bowel surgery (ClinicalTrials.gov). A third registry record that names ipamorelin, NCT07717866, is an observational study of 52 veterans in which ipamorelin is one of several supplements in a larger programme. That record does not test ipamorelin alone and listed no results when ClinicalTrials.gov was checked on 14 October 2026. The FDA found no professional society guideline that discusses ipamorelin for growth hormone deficiency or for post-surgery gut recovery (FDA briefing document, 29 October 2024).

How fast did growth hormone rise after ipamorelin in human volunteers?

In the one published study of ipamorelin in healthy volunteers found for this page, eight healthy men at each of five infusion rates, growth hormone rose to a single peak about 0.67 hours, or 40 minutes, after the infusion and then fell to negligible levels at every level tested; the study measured hormone and drug levels only (Gobburu et al., Pharmaceutical Research, 1999). In those eight men at each of five infusion rates, ipamorelin itself cleared quickly, with a terminal half-life of about 2 hours, a clearance of 0.078 litres per hour per kilogram and a steady-state volume of distribution of 0.22 litres per kilogram, in a study of hormone and drug levels in healthy men only (Gobburu et al., 1999).

This is a time course for a hormone, not a measure of how a person looks or feels. No study opened for this page followed people for weeks to see any physical change. The model that Gobburu et al. (1999) fitted to hormone levels in eight healthy men at each of five infusion rates also suggested that prolonged exposure may not keep stimulating growth hormone for long periods; that is a modelled result and not a measured long-term clinical outcome. The FDA flagged that point as a concern for people with partial growth hormone deficiency, whose stores of the hormone could run down; the concern comes from that model and is not a measured harm (FDA briefing document, 29 October 2024).

In male rats, with no count in the abstract, the half-life of ipamorelin was about 27 minutes by the intravenous route, and 60 to 80 percent of it left the body unchanged, mostly in urine; this is a rat measurement that does not establish a human result, as summarised in the FDA briefing document (Johansen et al., Xenobiotica, 1998). The two half-life numbers come from two species and two settings and should not be compared with each other.

What have studies found about ipamorelin and muscle?

None of the human studies found for this page measured muscle mass or strength after ipamorelin. The only muscle result found comes from rats. In 8-month-old female rats in a three-month steroid-induced model of muscle and bone loss, with no count in the abstract, rats that also received ipamorelin had higher maximum calf-muscle tension than rats given the glucocorticoid alone, and their bone formation rate rose four-fold; this describes one rat model and does not establish a human result (Andersen et al., Growth Hormone & IGF Research, 2001).

A second rat study points the same way. In rats given the steroid prednisolone, with no count in the abstract, ipamorelin counteracted the nitrogen wasting that the steroid caused, but less efficiently than growth hormone did in the same experiment; nitrogen balance is a measure of protein breakdown, not of muscle size, and this is a rat result that does not establish a human result (Aagaard et al., Growth Hormone & IGF Research, 2009).

A different compound in the same class gives a human reference point. In a 2-year trial of 65 healthy adults aged 60 to 81, the compound MK-677 raised fat-free mass by 1.1 kg over 12 months while it fell by 0.5 kg on placebo, and the gain did not change strength or function (Nass et al., Annals of Internal Medicine, 2008). MK-677 is a different molecule, and its results do not transfer to ipamorelin.

What have studies found about ipamorelin and body weight?

No human study found for this page measured weight loss after ipamorelin. In adult female rats over 15 days, body weight rose as exposure to ipamorelin rose, which is a rat result with no count in the abstract that does not establish a human result (Johansen et al., Growth Hormone & IGF Research, 1999). In mice, 2 weeks of ipamorelin raised body weight by about 15 percent and increased fat-pad weight and body fat, a mouse finding with no count in the abstract that does not establish a human result (Lall et al., Biochemical and Biophysical Research Communications, 2001). Ferrets given the cancer drug cisplatin lost about 24 percent less weight on the last day of a 72-hour study when also given ipamorelin, a ferret result with no count in the abstract that is not a human finding (Lu et al., Physiology & Behavior, 2024).

In growth-hormone-deficient and normal mice, ipamorelin was followed by higher leptin, a hormone made in fat tissue, and higher food intake, mouse results with no count in the abstract that do not establish a human result (Lall et al., 2001). The authors concluded that this class of compounds can raise body fat by routes that do not depend on growth hormone, possibly including more eating, in those mice (Lall et al., 2001). The rat study of surgical recovery also recorded higher food intake and body weight gain with repeated ipamorelin, in rats only, with no count in the abstract, and it does not establish a human result (Venkova et al., 2009).

A related approved medicine shows how a regulator treats the question. The US label for tesamorelin (Egrifta WR) lists an approved indication of excess abdominal fat in adults with HIV and lipodystrophy, and it states that the medicine is not indicated for weight loss management because it has a weight neutral effect (Egrifta WR label, revised March 2025; the label gives 2010 as the initial US approval year). How ipamorelin and tesamorelin differ covers the pair.

What do studies show about ipamorelin and testosterone?

No study found for this page measured testosterone in people given ipamorelin. The animal evidence is thin and comes from a fish. In a 21-day study in tilapia, serum luteinising hormone (LH, the pituitary signal to the testes) and 11-ketotestosterone, a fish androgen, rose and sperm cells developed further, a fish result with no count in the abstract that does not establish a human result (Gouda and Ganesh, Animal Reproduction Science, 2024). In pigs, none of the secretagogues tested, ipamorelin included, changed FSH or LH levels, an animal result with no count in the abstract that does not establish a human result (Raun et al., 1998). A 2020 review of the class names a gap in clinical data (Sinha et al., 2020).

The fish and pig results do not agree with each other, and neither answers the human question: LH rose in tilapia over 21 days but stayed flat in pigs (Gouda and Ganesh, 2024; Raun et al., 1998). The species differ, the routes differ, and the fish study ran for 21 days while the pig study measured short-term hormone levels. The FDA's 2024 review lists no testosterone outcome for ipamorelin. It notes that ghrelin receptors occur in the testis, which shows where the receptor is found and not what ipamorelin does there (FDA briefing document, 29 October 2024).

What do studies show about ipamorelin and the liver?

No study found for this page reports liver injury, liver enzymes or liver scans for ipamorelin in people. The FDA's 2024 review found no toxicity studies of ipamorelin with repeated exposure in the public literature (FDA briefing document, 29 October 2024). Both Phase 2 trials excluded people with significant liver disease, so they could not test ipamorelin in damaged livers (ClinicalTrials.gov NCT00672074 and NCT01280344). The adverse events the FDA listed from the 2014 surgery trial in 114 analysed bowel-surgery patients name no liver finding (FDA briefing document, 29 October 2024).

That list names low potassium, sleeplessness, high blood sugar, nausea, vomiting, belly swelling and two deaths in the 114 analysed bowel-surgery patients; a small postoperative trial cannot separate a drug effect from surgery, and the FDA said it is unclear whether ipamorelin played a part in the deaths (FDA briefing document, 29 October 2024). The trial of those 114 analysed bowel-surgery patients monitored laboratory tests, but the abstract and the FDA's summary report no liver result; absence from a summary is not proof of absence (Beck et al., 2014).

Two animal facts are relevant. In rats, ipamorelin left the body mainly through urine, while GHRP-6 left mainly through bile, a liver route; this is a rat measurement with no count in the abstract (Johansen et al., Xenobiotica, 1998). In rats given the steroid prednisolone, with no count in the abstract, adding ipamorelin lowered the liver's capacity to make urea by 20 percent and reduced the steroid's effect on urea-cycle genes, a change that the authors read as counteracting nitrogen wasting, in that rat model only, which does not establish a human result (Aagaard et al., 2009).

Has ipamorelin been studied together with tesamorelin?

No human study of tesamorelin and ipamorelin together was found in the PubMed and ClinicalTrials.gov searches conducted for this page on 14 October 2026. The PubMed search for both names returned seven records, all review articles, and ClinicalTrials.gov returned no study that lists both. Tesamorelin has its own trial record: in 412 adults with HIV and extra abdominal fat, visceral fat fell by 15.2 percent on tesamorelin and rose by 5.0 percent on placebo over 26 weeks, a result for tesamorelin alone in that group (Falutz et al., New England Journal of Medicine, 2007).

Falutz and colleagues studied tesamorelin alone against placebo in 412 adults with HIV, 86 percent of them men, under trial NCT00123253 (Falutz et al., 2007). In those 412 adults with HIV, IGF-1 rose by 81.0 percent on tesamorelin and fell by 5.0 percent on placebo, a tesamorelin-only result in one patient group (Falutz et al., 2007). In the same 412 adults with HIV and excess abdominal fat, adverse events did not differ significantly between the tesamorelin and placebo groups, though more people on tesamorelin withdrew because of one, in a trial that did not test ipamorelin (Falutz et al., 2007). The ipamorelin side effects page sets the safety records for the two compounds side by side.

What downsides have studies of ipamorelin recorded?

The human adverse-event sources examined for this page are a Phase 2 trial and the FDA's 2024 review. In the Phase 2 trial in 114 analysed bowel-surgery patients, low potassium (12.5 percent against 3.4 percent), sleeplessness (10.7 against 5.2 percent) and high blood sugar at discharge (14.3 against 8.6 percent) were more common with ipamorelin than with placebo, in a small trial that cannot separate a drug effect from surgery (Beck et al., 2014; FDA briefing document, 29 October 2024). In that trial of 114 bowel-surgery patients, two patients given ipamorelin died after surgical complications, and the FDA said it is unclear whether ipamorelin played a part (FDA briefing document, 29 October 2024, describing Beck et al., 2014). The FDA also lists immunogenicity, the chance of antibodies against the peptide, as an open concern (FDA briefing document, 29 October 2024).

The full list, with the FDA's category 2 listing and the regulator's reasoning, is on the ipamorelin side effects page. That page also covers what is known about products sold outside trials. What peptides do in general, and what studies found puts ipamorelin in the wider field.